Periodic Reporting for period 2 - EHAWEDRY (Energy harvesting via wetting/drying cycles with nanoporous electrodes)
Período documentado: 2022-07-01 hasta 2023-12-31
The EHAWEDRY concept is based on the hypothesis that the area of contact between electrolyte solution and a nanoporous electron-conducting material can be effectively reduced via (waste)-heat-induced solvent evaporation from the material surface. Then, the EDL capacity can be charged (by an external source) in the fully wet state, the external electricity source can be disconnected and the solvent can be partially evaporated. The corresponding reduction of capacity gives rise to increasing voltage. When the capacitor is discharged at a higher voltage, there are energy gains.
Huge amounts of energy are lost during conversion, transportation and end use. Most of this is in the form of heat. Its exploitation requires its conversion into more manageable forms, such as electricity. While a number of methods exist to convert waste heat to mechanical work and eventually to electricity they are not cost-effective for a highly distributed recovery of waste heat nor for the conversion of low-grade waste heat, which accounts for well above 50 % of the total.
It is expected that EHAWEDRY technology can reach volumetric power densities comparable to the established waste heat recovery technologies. However, EHAWEDRY technology, based on electrochemical capacitors instead of pressurized chambers, expanders, compressors and turbines, has the critical potential advantages of a lower cost, larger flexibility of design, and broad scalability.
The overall objective of the EHAWEDRY project is obtaining a proof of concept of the proposed new technology.
Huge amounts of energy are lost during conversion, transportation and end use. Most of this is in the form of heat. Its exploitation requires its conversion into more manageable forms, such as electricity. While a number of methods exist to convert waste heat to mechanical work and eventually to electricity they are not cost-effective for a highly distributed recovery of waste heat nor for the conversion of low-grade waste heat, which accounts for well above 50 % of the total.
It is expected that EHAWEDRY technology can reach volumetric power densities comparable to the established waste heat recovery technologies. However, EHAWEDRY technology, based on electrochemical capacitors instead of pressurized chambers, expanders, compressors and turbines, has the critical potential advantages of a lower cost, larger flexibility of design, and broad scalability.
The overall objective of the EHAWEDRY project is obtaining a proof of concept of the proposed new technology.
A boundary value problem was formulated and numerically solved for the dynamics of EDL formation at two identical ideally polarizable porous electrodes. We considered the dynamics of advancing and receding menisci and mechano-electrical energy conversion. To address the problem of receding and advancing contact angle dynamics and possible wetting-film formation, we conducted molecular-dynamic simulations.
Carbon nanoporous monoliths were fabricated in a two-step synthesis process. Crack-free and mechanically stable monolithic nanoporous carbons able to adsorb water could be obtained. A parallel approach used renewable carbon sources (biomass). We have also used MnO2 as an ideal pseudo-capacitive cathode material and developed a hydrothermal synthesis route for the production of d-MnO2 with a 2D laminar structure.
We used a vacuum-assisted particle self-assembly procedures to produce porous layers with proper mechanical, structural and hydrophobicity/phobicity properties.
We studied imbibition dynamics by gravimetric and optical techniques. We clearly demonstrated that the imbibition front stops at a specific height, which indicates that considerable partial drying of nanoporous samples is possible even in hydraulic contact with liquid. In preliminary experiments on imbibition using nanoporous carbons we observed appearance of considerable transient voltages and currents.
Synchrotron-based small-angle X-ray diffraction experiments demonstrated that drying and imbibition dynamics can be resolved very precisely by SAXS measurement, whereas the movement of ions can be detected by their fluorescence signal. However, so far the results did not show the expected feature of sharp boundaries between counter-ion-rich and counter-ion-free parts of the sample. The lack of sharp boundaries has also been observed in experiments on drying of Vycor glass using NMR imaging.
Measurements of water adsorption/desorption by nanoporous glasses pre-equilibrated with electrolyte solutions have revealed considerable differences from the pure-water behaviour. To better understand the properties of hypothetical adsorption water films in contact with menisci, we performed measurements of electrical conductivity of precursor films between closely positioned sessile water/salt-solution droplets. We have started fabrication of nanofluidic devices that will enable future studies of imbibition and drying kinetics in individual nanochannels.
In partial-electrode-emersion experiments, we demonstrated voltage increases in response to mechanical actuation of contact area between charged ideally-polarizable electrodes and electrolyte solutions.
Two novel experimental approaches were used for the determination of surface-charge density in nanopores. Its values were used for estimates of power density in energy harvesting from water evaporation.
In view of the fundamental uncertainties concerning the feasibility of the proposed concept, we have also explored several related scenarios.
We discovered that wetting of a nanoporous electrode material can give rise to significant transient voltages and currents.
We evaluated the potentialities of electrokinetic energy harvesting from evaporation. The process can be used for energy harvesting in water-evaporation air conditioning optionally accompanied by hydrogen generation.
Based on the hypothesis that electroosmosis can occur along the surface of hydrophilic pores even when they are not completely filled with water, we conceived a principally new electrically-driven dehumidification process.
Carbon nanoporous monoliths were fabricated in a two-step synthesis process. Crack-free and mechanically stable monolithic nanoporous carbons able to adsorb water could be obtained. A parallel approach used renewable carbon sources (biomass). We have also used MnO2 as an ideal pseudo-capacitive cathode material and developed a hydrothermal synthesis route for the production of d-MnO2 with a 2D laminar structure.
We used a vacuum-assisted particle self-assembly procedures to produce porous layers with proper mechanical, structural and hydrophobicity/phobicity properties.
We studied imbibition dynamics by gravimetric and optical techniques. We clearly demonstrated that the imbibition front stops at a specific height, which indicates that considerable partial drying of nanoporous samples is possible even in hydraulic contact with liquid. In preliminary experiments on imbibition using nanoporous carbons we observed appearance of considerable transient voltages and currents.
Synchrotron-based small-angle X-ray diffraction experiments demonstrated that drying and imbibition dynamics can be resolved very precisely by SAXS measurement, whereas the movement of ions can be detected by their fluorescence signal. However, so far the results did not show the expected feature of sharp boundaries between counter-ion-rich and counter-ion-free parts of the sample. The lack of sharp boundaries has also been observed in experiments on drying of Vycor glass using NMR imaging.
Measurements of water adsorption/desorption by nanoporous glasses pre-equilibrated with electrolyte solutions have revealed considerable differences from the pure-water behaviour. To better understand the properties of hypothetical adsorption water films in contact with menisci, we performed measurements of electrical conductivity of precursor films between closely positioned sessile water/salt-solution droplets. We have started fabrication of nanofluidic devices that will enable future studies of imbibition and drying kinetics in individual nanochannels.
In partial-electrode-emersion experiments, we demonstrated voltage increases in response to mechanical actuation of contact area between charged ideally-polarizable electrodes and electrolyte solutions.
Two novel experimental approaches were used for the determination of surface-charge density in nanopores. Its values were used for estimates of power density in energy harvesting from water evaporation.
In view of the fundamental uncertainties concerning the feasibility of the proposed concept, we have also explored several related scenarios.
We discovered that wetting of a nanoporous electrode material can give rise to significant transient voltages and currents.
We evaluated the potentialities of electrokinetic energy harvesting from evaporation. The process can be used for energy harvesting in water-evaporation air conditioning optionally accompanied by hydrogen generation.
Based on the hypothesis that electroosmosis can occur along the surface of hydrophilic pores even when they are not completely filled with water, we conceived a principally new electrically-driven dehumidification process.
Previous molecular-simulation studies have not addressed the crucial issue of adsorption films of water in contact with advancing/receding triple-contact lines. A mathematical model for Electric Double Layer propagation inside nano-porous electrodes was developed to establish the hierarchy of relaxation times in charging ideally polarizable porous electrodes.
We synthesized new nanoporous polymer and carbon monoliths with 3D pore structures and well-defined pore sizes. For that, we developed a new and general synthesis protocol.
We produced carbon-based materials with controlled porosity from biomass sources, two-dimensional MnO2 nanoparticles and carbon/MnO2 composites using novel low-cost precursors and low-energy processes. We also generated new porous composite layers with beyond SOTA control over their hydrophobic/philic properties.
Drying and spontaneous imbibition of nanoporous materials have barely been previously explored with aqueous electrolytes. We performed pioneering experiments on monolithic nanoporous carbons demonstrating that it is possible to monitor capillarity-driven flows and drying via monitoring electrical current, charge and voltage evolution.
Through optical experiments on transparent model nanoporous membranes, we investigated the underlying thermodynamic and kinetic phenomena of pore filling/emptying by vapour water in the presence of confined salts.
We have experimentally confirmed the possibility of energy harvesting via mechanical actuation of contact area with smooth macroscopic electrodes. We obtained unique quantitative information on the surface-charge density in nanopores and made realistic estimates of power densities in systems for energy harvesting via water evaporation from nanoporous materials.
In summary, the feasibility of project concept has been demonstrated for some model systems but problems have been encountered with extending this to nanoporous materials. Therefore, for the future R&D, it is proposed to combine continued investigation of the project concept with exploration of the identified related scenarios. Similarly to the original EHAWEDRY concept, these scenarios can have considerable socio-economic impact and wider societal implications. Besides, materials and methods to be used are close to those considered for the original project concept.
We synthesized new nanoporous polymer and carbon monoliths with 3D pore structures and well-defined pore sizes. For that, we developed a new and general synthesis protocol.
We produced carbon-based materials with controlled porosity from biomass sources, two-dimensional MnO2 nanoparticles and carbon/MnO2 composites using novel low-cost precursors and low-energy processes. We also generated new porous composite layers with beyond SOTA control over their hydrophobic/philic properties.
Drying and spontaneous imbibition of nanoporous materials have barely been previously explored with aqueous electrolytes. We performed pioneering experiments on monolithic nanoporous carbons demonstrating that it is possible to monitor capillarity-driven flows and drying via monitoring electrical current, charge and voltage evolution.
Through optical experiments on transparent model nanoporous membranes, we investigated the underlying thermodynamic and kinetic phenomena of pore filling/emptying by vapour water in the presence of confined salts.
We have experimentally confirmed the possibility of energy harvesting via mechanical actuation of contact area with smooth macroscopic electrodes. We obtained unique quantitative information on the surface-charge density in nanopores and made realistic estimates of power densities in systems for energy harvesting via water evaporation from nanoporous materials.
In summary, the feasibility of project concept has been demonstrated for some model systems but problems have been encountered with extending this to nanoporous materials. Therefore, for the future R&D, it is proposed to combine continued investigation of the project concept with exploration of the identified related scenarios. Similarly to the original EHAWEDRY concept, these scenarios can have considerable socio-economic impact and wider societal implications. Besides, materials and methods to be used are close to those considered for the original project concept.